Expert: Jim Hyland - 7/26/2006

Question
Help! Bagworms are devouring my beautiful Colorado Blue Spruce.  I have picked off as many as I could but can�t reach perhaps half of them on the tree. I have tried spraying with Liquid Sevin (not much success) and yesterday I sprayed with Ortho Systemic Insect Killer (8% Acephate), but I still see the worms chomping on the needles and setting up home.  How can I kill these critters when they have surrounded themselves in their bags?

Answer
The key to controlling older bagworms in the larger bags is to make sure all the foliage is throughly wet with the spray. Insecticides recommended for controlling bagworms include Bacillus thuringiensis kurstaki (sold as Dipel or Thuricide), cyfluthrin (Tempo and in some Bayer products) and spinosad (Conserve and some Ferti-lome products). Insecticide sprays are effective against the young larvae but bags that are 3/4 inch long or longer are very difficult to control. The bacterium Bacillus thuringiensis is effective on young caterpillars, but the material must be ingested--so thorough plant coverage is essential. Spinosad works very effectively by contact and ingestion. Cyfluthrin is recommended for larger larvae, but again thorough coverage is essential.